1. Technical Field
The present invention relates to a technique for driving an electrophoretic device.
2. Related Art
JP-A-2002-149115 discloses a related art of an active matrix electrophoretic device. According to this related art, an electrophoretic device drives pixels using a driving method called a two-step writing method by means of pixel circuits each including a single transistor and a single capacitor (i.e., 1T1C pixel circuits). According to the two-step writing method, a voltage for white display (or black display) is written into each pixel (in order to erase the display of each pixel) and, after that, a voltage for white display (or a voltage for black display) is appropriately written into the pixels in accordance with display data, thus forming an image, such as a picture or characters. As for erase operations, writing a voltage for white display into each pixel is called “whole white erasure” and writing a voltage for black display into each pixel is called “whole black erasure.
In typical electrophoretic devices utilizing the above-described whole white erasure or whole black erasure, however, each erase operation requires approximately one second. It is disadvantageous in terms of a reduction in image rewrite time. When the whole white erasure and whole black erasure are used in combination in order to prevent image lag, the combined erase operation requires two or more seconds. It is more disadvantageous. One of related-art approaches whereby the above-described disadvantages can be avoided is a simultaneous writing method using the above-described 1T1C pixel circuits. The simultaneous writing method has no erase operation before writing a voltage into each pixel. There is no problem from the viewpoint of the image rewrite time. However, this method requires a power source providing a large potential difference. Disadvantageously, it results in an increase in power consumption of the electrophoretic device. This disadvantage is significant because the electrophoretic device offers or is expected to offer an advantage in that the power consumption is low. According to another related art, an electrophoretic device includes a latch circuit that is incorporated into each pixel circuit. The latch type electrophoretic device needs many (for example, five) transistors in each pixel circuit. Disadvantageously, this arrangement may easily cause a reduction in yield.